Tap on the Cc/Bcc, From: line where it shows the image size
Then select a smaller file size before emailing.
Here is the original demo I made emailed at it's smallest size.
No tool has everything, and while I'm not going to cry if/when Skitch adds a resize option, I'm not going to miss it much until then. For what it does, nothing else I've tried on the iPad is as quick and easy to use; and when it comes to jotting up a screen shot to illustrate something, quick and easy triumphs a absolute control. For me anyway.
If I need absolute control of an image, I'd probably take the time to copy it to the computer and use the far better tools I have there.